A mechanical system is a tuned network, the response of which is dependent upon mass, stiffness, and damping. When a system is not tuned properly, periodic or aperiodic torques may produce torsional vibrations. Excessive torsional vibrations may cause such detrimental effects as broken shafts, mutilated gears, and cracks in couplings and flange bolts. However unlike translational vibrations, which cause noise and shaking that are easy to detect, torsional vibrations are difficult to detect because the vibrations are generally not noticed until a component breaks down.
One method that attempts to detect torsional vibration is described in a "Technology Interchange" publication published by the Vibration Institute entitled, "Torsional Vibration Measurements in the Preventive Maintenance of Rotating Machinery" authored by Harold Hershkowitz. Here, a magnetic pickup sensor is used to produce an input signal that has a frequency proportional to the angular velocity of a rotating shaft. The input signal is delivered to a Frequency-to-Voltage convertor that produces an output voltage proportional to the shaft velocity. The fluctuations in the output voltage represent the torsional velocity of the shaft. The fluctuations in the output voltage is integrated to produce an angular displacement signal that is representative of the torsional vibration.
However, the angular displacement signal includes spurious signal components that have nothing to do with the torsional vibration. Thus, the unwanted components must be filtered-out or attenuated using high and low pass filters. Unfortunately, the filters that adequately attenuate the unwanted components do so in a slow fashion as compared to the torsional vibrational response of the system. Thus, much of the data produced by such a measurement system is erroneous and not acceptable for design and analysis purposes.
The present invention is directed to overcoming one or more of the problems as set forth above.